858 research outputs found
Silicon Tetrafluoride on Io
Silicon tetrafluoride (SiF4) is observed in terrestrial volcanic gases and is
predicted to be the major F - bearing species in low temperature volcanic gases
on Io (Schaefer and Fegley, 2005b). SiF4 gas is also a potential indicator of
silica-rich crust on Io. We used F/S ratios in terrestrial and extraterrestrial
basalts, and gas/lava enrichment factors for F and S measured at terrestrial
volcanoes to calculate equilibrium SiF4/SO2 ratios in volcanic gases on Io. We
conclude that SiF4 can be produced at levels comparable to the observed
NaCl/SO2 gas ratio. We also considered potential loss processes for SiF4 in
volcanic plumes and in Io's atmosphere including ion-molecule reactions,
electron chemistry, photochemistry, reactions with the major atmospheric
constituents, and condensation. Photochemical destruction (tchem ~ 266 days)
and/or condensation as Na2SiF6 (s) appear to be the major sinks for SiF4. We
recommend searching for SiF4 with infrared spectroscopy using its 9.7 micron
band as done on Earth.Comment: 16 pages, 2 figures, 1 table; Icarus, in pres
A feasibility study of wearable activity monitors for pre-adolescent school-age children.
IntroductionUnderstanding physical activity is key in the fight against childhood obesity. The objective of this study was to examine the feasibility of using certain wearable devices to measure physical activity among children.MethodsA qualitative study was conducted with 25 children aged 7 to 10 years to assess acceptability and compliance of wearable activity devices in this age group. During March through August 2012, children participated in a 4-week study of 3 accelerometer models and a heart rate monitor. Children were asked to use a different device each week for 7 consecutive days. Children and their parents completed structured interviews after using each device; they also completed a final exit interview.ResultsThe wrist-worn Polar Active was the device most preferred by children and was associated with the highest level of compliance. Devices that are comfortable to wear, fit properly, have engaging features, and are waterproof increase feasibility and are associated with higher levels of compliance.ConclusionThe wrist-worn device was the most feasible for measuring physical activity among children aged 7 to 10 years. These findings will inform researchers in selecting tools for measuring children's physical activity
Alkali and Halogen Chemistry in Volcanic Gases on Io
We use chemical equilibrium calculations to model the speciation of alkalis
and halogens in volcanic gases emitted on Io. The calculations cover wide
temperature (500-2000 K) and pressure (10^-6 to 10^+1 bars) ranges, which
overlap the nominal conditions at Pele (T = 1760 K, P = 0.01 bars). About 230
compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are
considered. We predict the major alkali and halogen species in a Pele-like
volcanic gas and the major alklai and halogen condensates. We also model
disequilibrium chemistry of the alkalis and halogens in the volcanic plume.
Based on this work and our prior modeling for Na, K, and Cl in a volcanic
plume, we predict the major loss processes for the alkali halide gases are
photolysis and/or condensation onto grains. On the basis of elemental
abundances and photochemical lifetimes, we recommend searching for gaseous KCl,
NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during
eruptions. Based on abundance considerations and observations of brown dwarfs,
we also recommend a search of Io's extended atmosphere and the Io plasma torus
for neutral and ionized Li, Cs, Rb, and F.Comment: 32 pages, 4 tables, 5 figures; accepted for publication by Icaru
Atmospheric Chemistry of Venus-like Exoplanets
We use thermodynamic calculations to model atmospheric chemistry on
terrestrial exoplanets that are hot enough for chemical equilibira between the
atmosphere and lithosphere, as on Venus. The results of our calculations place
constraints on abundances of spectroscopically observable gases, the surface
temperature and pressure, and the mineralogy of the surface. These results will
be useful in planning future observations of the atmospheres of
terrestrial-sized exoplanets by current and proposed space observatories such
as the Hubble Space Telescope (HST), Spitzer, James Webb Space Telescope
(JWST), Terrestrial Planet Finder, and Darwin.Comment: 35 pages, 4 figures, 3 tables; 1 appendix; submitted to ApJ; version
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